1. Field of the Invention
The present invention relates to a multi-chip module (call MCM hereafter), and more particularly to an MCM wherein a conventional thermal pillar is eliminated.
2. Description of the Prior Art
FIG. 2 shows a cross-sectional view of a conventional three-layered MCM having a typical thermal pillar. The thermal pillar consists of patterned metal layers 2a.about.2cand each vertical metal column 7 on them penetrating each polyimide film 3. Heat generated by semiconductor chips 6 is collected by an uppermost metal layer 2d of the multi-layered interconnection circuits, through intermediate layers 4 and 5, and transfered by the thermal pillar to the patterned bottom metal layer 2a in the lowest layer to be dissipated into an electrically insulating substrate 1. A conventional thermal pillar is usually fabricated, layer by layer, by repeating a series of processing steps for each circuit layer. It comprises steps of depositing each metal layer 2a.about.2c on each insulating layer 3a.about.3c, forming a metal column 7 by selective plating, patterning of the metal layer by anisotropic etching, forming a polyimide layer over the metal column 7, and polishing it for planarization. These are mostly extra processing steps, and particularly, the selective plating of metal column 7 is not compatible to processing steps for the multi-layered interconnection circuits. Furthermore, this is costly and time-consuming work, which has been a long-time obstacle for simplifying the fabrication process of MCM's.